1. Technical Field
The invention is related to transformerless DC-DC power converters and in particular to transformerless DC-DC voltage amplifiers having a large voltage gain ratio.
2. Background Art
DC-DC power converters are well-known in the art. Typically, in order to raise a voltage level of a power supply, a bank of capacitors are each charged in parallel with the supply voltage and are then discharged in series to a load. This technique is disclosed in U.S. Pat. No. 4,654,769, for example. Such a device operates in two phases, a first phase during which all the capacitors are charged in parallel while being connected to the supply voltage, and a second phase in which the capacitors are disconnected from the supply voltage and are connected together in series across the load. The voltage increase ratio is equal to the number of capacitors. The foregoing concept is also disclosed in U.S. Pat. No.'s 3,818,309; 4,460,952; 4,321,661; and 4,047,091. In one variation of this technique, several banks of capacitors are charged separately and then all of the capacitors are discharged across the load simultaneously, as disclosed in U.S. Pat. No. 3,579,074. All of the foregoing disclose multiplying the voltage by a factor N equal to the number of capacitors.
A voltage divider may be constructed in a similar manner by reversing the operation, or in other words charging the capacitors in parallel across the supply and discharging them in series across the load, as disclosed in U.S. Pat. No. 3,505,586. As another example of a voltage divider circuit, the dividing ratio is increased by cascading successive stages of capacitor pairs. Each capacitor pair is charged in series by the preceding stage of a capacitor pair and then is discharged in parallel to the succeeding stage of a capacitor pair, as disclosed in U.S. Pat. No. 3,863,135. In this technique, N stages of capacitor pairs provides a voltage reduction of 2.sup.N.
The present invention is concerned with problems in high voltage amplification in a DC-DC power converter. The problem with the prior art technique of increasing a voltage using a bank of capacitors is that the voltage gain is necessarily limited by a tendency of high voltages to couple through and thereby paralyze the secondary control switching network which regulates the operation of the capacitor bank. Accordingly, devices which increase the voltage by charging the capacitors in parallel and discharging them in series across the load necessarily were limited in the ratio by which the voltage could be raised. Thus, a single bank of capacitors of limited size sufficed to perform a necessarily limited voltage increase function. Because of the tendency of a voltage which has been boosted by several factors of ten to leak or couple through the switching network controlling the capacitors to the supply, it does not seem possible to achieve a large voltage gain and a DC-DC power converter.
Accordingly, it is the object of the present invention to provide a DC-DC power converter which amplifies the voltage with far higher gains than heretofore accomplished in the prior art. It is a further object of the invention to achieve the foregoing without undue leakage of the high voltage back to the power supply through the switching network. It is a further object of the invention to achieve a large voltage gain ratio in such a device without a corresponding increase in the number of capacitors required to be switched.